It has been known in the art that fine metallic powder reacts with atmospheric oxygen in the presence of water, and this principle can be found in various disoxidants which have thus far been proposed and used widely for the purpose of food preservation. For example, Japanese Laid-Open Patent Application No. 52-104486 proposes a disoxidant consisting of a mixture of a metal and a filler, Japanese Laid-Open Patent Application No. 52-104489 proposes a disoxidant consisting of a metal, water, a halogenated metal and a filler, and Japanese Laid-Open Patent Application No. 53-14185 proposes a disoxidant consisting of metal powder coated with a halogenated metal.
In this connection, there are two methods available for industrially producing a disoxidant which contains fine metal powder as a major component with disoxidation activity. The first method is to prepare a master batch by mixing the respective components beforehand, charging and sealing a predetermined amount of the master batch in packaging bags by the use of a charging machine. The second method is to charge successively predetermined amounts of the ingredients in the packaging bag by a charging machine. The first method has an advantage that the respective components can be mixed by means of a mixing machine like a kneader or an internal mixer to attain a relatively good mixing effect to permit production of a disoxidant with high reactivity. However, there unavoidably arises a problem that the fine metallic powder which has a far greater specific gravity as compared with other components so that it is extremely difficult to obtain a perfectly uniform mixture by mixing it with other ingredients, resulting in irregularities in the amounts of the fine metallic powder charged in individual packaging bags. Since the oxygen absorption capacity of the disoxidant is determined by the content of the fine metallic powder, it will invite irregularities in the disoxidation capacity of the ultimate products. Besides, the first method requires to conduct the operations in an inert gas atmosphere to prohibit inducement of disoxidation reaction in the course of preparation of the master batch.
On the other hand, the second method is free of the problem concerning the irregularities in the oxygen absorption capacity since predetermined amounts of the respective components are securely charged in the individual packaging bags. In this instance, however, it is difficult to mix the respective components unformly, and a portion mainly consisting of the metal powder and a portion mainly consisting of a filler material separately exist in the packaging bags. Upon reaction in the presence of water, the metallic powder tends to aggregate into blocks which are extremely hinderous to smooth progress of the disoxidation reaction. In this regard, Japanese Laid-Open Patent Application No. 54-35189 discloses a method of successively charging metal powder and a hydrous substance into packaging paper without contacting them with each other prior to the charging stage. Nevertheless, even this method fails to attain the uniform mixing of the metal powder and hydrous substance. Namely, according to this method, the hydrous substance is preferred to be in a granular form having a particle size as large as 0.5-10 mm, which conspicuously differs from that of the metal powder and thus it is impossible to form a uniform mixture with the metal powder. The major portion of the metal powder remains separate from the granules in most portions so that there cannot be obtained a disoxidant with enhanced reactivity.